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Temp4.2 C
RH18 %
WindN 18 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

858
FXHW60 PHFO 291333
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
333 AM HST FRI APR 29 2016

.SYNOPSIS...
A STRONG HIGH PRESSURE RIDGE NORTH OF THE AREA WILL KEEP TRADE
WINDS LOCALLY BREEZY TODAY AND TONIGHT. TRADES WILL WEAKEN
SLIGHTLY ON SATURDAY AS A WEAK FRONT PASSES FAR NORTH OF THE
STATE...THEN A NEW HIGH WILL BUILD IN TO OUR NORTH SATURDAY NIGHT
THROUGH MONDAY WITH TRADES STRENGTHENING ONCE AGAIN. THE TRADES
WILL FOCUS SHOWERS PRIMARILY OVER WINDWARD SLOPES...WITH A FEW
SHOWERS SPILLING OVER INTO LEEWARD AREAS MAINLY DURING THE LATE
NIGHT AND EARLY MORNING HOURS. SHOWERS WILL ALSO REMAIN POSSIBLE
EACH AFTERNOON OVER THE LEE SLOPES OF THE BIG ISLAND. SHOWERS MAY
INCREASE TOWARD THE MIDDLE OF NEXT WEEK AS MOISTURE FROM THE
REMNANTS OF AN OLD FRONT MOVES THROUGH THE STATE.

&&

.DISCUSSION...
TRANQUIL TRADE WIND WEATHER PREVAILS ACROSS HAWAII ON THIS
EARLY FRIDAY MORNING. RADAR SHOWS SCATTERED LIGHT SHOWERS MOVING
EAST TO WEST WITHIN THE TRADE FLOW...BUT RAIN GAUGE DATA SHOWS
ONLY A FEW WINDWARD STATIONS RECEIVING ANY MEASURABLE RAINFALL
DURING THE PAST SEVERAL HOURS. SURFACE ANALYSIS DEPICTS A 1029 MB
HIGH CENTERED ABOUT 1400 MILES NE OF PHNL...WITH A RIDGE EXTENDING
WESTWARD TO THE NORTH OF THE STATE...AND A COLD FRONT FAR TO THE
NW NEAR MIDWAY ATOLL. ALOFT...A MID/UPPER LEVEL RIDGE IS CENTERED
A FEW HUNDRED MILES NE OF THE STATE...WITH A VERY DRY/STABLE
AIRMASS OVER HAWAII. MIMIC-TPW SATELLITE IMAGERY SHOWS A
GENERALLY DRY AIRMASS OVER AND AROUND THE STATE...WITH ESTIMATED
PWATS BETWEEN 1 AND 1.2 INCHES. THE 12Z SOUNDINGS ALSO SHOW A DRY
AND STABLE AIRMASS IN PLACE...WITH PWATS JUST OVER ONE INCH AND
STRONG INVERSIONS BASED BETWEEN 7000 AND 8000 FEET.

LITTLE CHANGE TO THE ONGOING TRADE WIND WEATHER PATTERN IS
EXPECTED THROUGH THE NEXT SEVERAL DAYS. BREEZY TRADES WILL PERSIST
TODAY INTO TONIGHT AS THE RIDGE HOLDS FIRM TO OUR NORTH...THEN
SHOULD WEAKEN SLIGHTLY LATE TONIGHT AND SATURDAY AS THE WEAK COLD
FRONT CURRENTLY NEAR MIDWAY PASSES BY WELL TO OUR NORTH. A NEW
HIGH IS THEN FORECAST TO BUILD NORTH OF THE STATE SATURDAY NIGHT
THROUGH MONDAY...WHICH WILL CAUSE TRADE WINDS TO INCREASE ONCE
AGAIN. SHOWERS AND CLOUDS WILL CONTINUE TO FAVOR MAINLY WINDWARD
SECTIONS...ESPECIALLY DURING THE NIGHT AND EARLY MORNING HOURS.
THERE WILL ALSO BE THE CHANCE FOR WIDELY SCATTERED SHOWERS EACH
AFTERNOON AND EARLY EVENING ON THE KONA SLOPES. PERSISTENT RIDGING
ALOFT WITH ONLY SHALLOW MOISTURE AVAILABLE WILL KEEP MOST OF THE
SHOWER ACTIVITY ON THE LIGHT SIDE.

AS THE SURFACE HIGH SHIFTS SLOWLY EASTWARD TO OUR NORTH NEXT
WEEK...MODELS SHOW MOISTURE FROM THE DISSIPATED FRONTAL REMNANTS
GETTING CAUGHT UP IN THE TRADE WIND FLOW AND EVENTUALLY MOVING
SW ACROSS THE ISLANDS. THE LAST FEW MODELS RUNS HAVE COME INTO
BETTER AGREEMENT ON THE TIMING OF THIS...SHOWING THE STRIPE OF
ENHANCED MOISTURE REACHING THE STATE TUESDAY AFTERNOON AND MOVING
ACROSS THE AREA THROUGH WEDNESDAY EVENING. HAVE INCREASED RAIN
CHANCES SOMEWHAT FOR THOSE TIME PERIODS...WITH MORE SHOWERS
SPILLING OVER INTO LEEWARD AREAS ESPECIALLY DURING THE NIGHTTIME
HOURS.

&&

.AVIATION...
MODERATE TO FRESH TRADE WINDS WILL FOCUS CLOUDS AND LIGHT SHOWERS
OVER THE WINDWARD AND MAUKA AREAS. AIRMET TANGO REMAINS IN EFFECT
FOR TEMPO MODERATE LOW LEVEL TURB OVER AND IMMEDIATELY S THROUGH W
OF THE MOUNTAINS DUE TO THE TRADES. CONDITIONS ARE EXPECTED TO
IMPROVE TOWARDS AFTERNOON.

TEMPO MVFR CIGS MAY DEVELOP EARLY THIS MORNING ALONG WINDWARD
SLOPES AND COASTS. AIRMET SIERRA HAS BEEN ISSUED FOR ANTICIPATED
MTN OBSCURATION CONDITIONS ALONG NORTHEAST FACING SLOPES OF THE
BIG ISLAND.

&&

.MARINE...
THE OVERNIGHT ASCAT PASS FOUND 25 KT WINDS IN THE ALENUIHAHA
CHANNEL AND SOUTHWEST OF THE BIG ISLAND...AND SOLID 20 KT WINDS
NORTH OF MAUI AND MOLOKAI. WE HAVE EXTENDED THE EXISTING SMALL
CRAFT ADVISORY /SCA/ THROUGH 6 AM SATURDAY MORNING FOR THE
TYPICALLY WINDY WATERS AROUND MAUI COUNTY AND THE BIG ISLAND...
EXCEPT FOR THE WATERS SE OF THE BIG ISLAND WHICH HAVE BEEN DROPPED
FROM THE ADVISORY. WINDS MAY DROP BRIEFLY BELOW SCA CRITERIA
ACROSS ALL WATERS ON SATURDAY...BUT WITH A NEW HIGH PRESSURE AREA
STARTING TO BUILD NORTH OF THE STATE SATURDAY NIGHT INTO SUNDAY
IT APPEARS LIKELY THAT SCA CONDITIONS WILL RETURN TO THE TYPICALLY
WINDY AREAS THEN. ADVISORY CONDITIONS MAY BECOME MORE WIDESPREAD
BY EARLY NEXT WEEK AS THE NEXT HIGH STRENGTHENS AND MOVES SLOWLY
EASTWARD TO THE NORTH OF THE STATE.

THE HILO...PAUWELA AND MOKAPU POINT BUOYS ALL SHOW SHORT PERIOD
SEAS OF 7-8 FEET DUE TO TRADE WIND SWELL. THIS SWELL SHOULD
CONTINUE TODAY THEN DECREASE SLIGHTLY ON SATURDAY. TRADE WIND
SWELL SHOULD THEN INCREASE AGAIN EARLY NEXT WEEK AS THE NEXT HIGH
BUILDS NORTH OF THE AREA. SMALL SWELLS FROM THE NORTHWEST WILL
CONTINUE THROUGH THE WEEKEND. SURF ALONG SOUTH FACING SHORES
SHOULD INCREASE SOMEWHAT DURING THE WEEKEND AND INTO EARLY NEXT
WEEK AS A SWELL FROM EAST OF NEW ZEALAND REACHES THE ISLANDS.
OVERALL...EXPECT SURF TO REMAIN BELOW ADVISORY LEVELS ON ALL
SHORES THROUGH THE WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 AM HST SATURDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS.

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...BEDAL

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office